Conventionally, for a silver halide photographic material (hereinafter referred to as a photographic material), its support is required to be transparent and excellent in film strength. As materials that meet these requirements, nitrocellulose and triacetyl cellulose belonging to cellulose series, are used, and in recent years, polyethylene terephthalates have been rapidly introduced.
Since polyethylene terephthalates are excellent in water-resistance and film strength, they are useful for attaining dimensional stability and reduction in film thickness.
However, polyethylene terephthalates have the defect that when the film of a polyethylene terephthalate is kept in a rolled state for a long period of time or is exposed to a high temperature (e.g., in a car in midsummer), it is highly apt to undergo a core set curl.
To eliminate this defect, JP-A ("JP-A" means unexamined published Japanese patent application) No. 51174/1975 describes that a roll of a polyethylene terephthalate film is exposed for 24 hours or more to an atmosphere whose temperature is kept 15.degree. to 35.degree. C. higher than the temperature at which the film has been rolled on a slit roll. Further, JP-A No. 95374/1975 suggests that a polyester film (a polyethylene terephthalate film is described), which has been biaxially stretched and then heat set, is aged by heating it at a temperature ranging from 40.degree. to 130.degree. C., so that the flatness may be improved. However, even if it is attempted to eliminate core set curl by these heat treatments, when the roll is left for a long period of time at the above-described high temperature (80.degree. C. or over), the attempt has no effect at all, which is a practical problem. That is, when a color negative film, whose support is made of a polyethylene terephthalate that has been heat-treated under the above-described conditions, is wound into a cartridge (magazine or Patrone) for usual 35-mm film, and then it is allowed to stand at 80.degree. C. for 2 hours and is cooled, the film removed from the cartridge has core set curl resembling the shape of the cartridge, showing no effect of the heat treatment at all. As a result, it causes transportation trouble in an automatic processor and is apt to curl during the printing, which may cause problems.
U.S. Pat. No. 4,141,735 and JP-A No. 95374/1975 suggest means of further eliminating core set curl by heat treatment. These techniques are clearly effective against core set curl, especially in the case of storage at high temperatures, and they resolve substantially the problem of core set curl.
However, the polyethylene naphthalate, which was used in the means described in U.S. Pat. No. 4,147,735, has the problem that it has absorption and fluorescence-emission in the ultraviolet region, leading to discoloration such as yellowing over time and fogging with regard to photographic properties.
Although, as means of incorporating an ultraviolet absorbent in a polyester, JP-A Nos. 247451/1989 and 247452/1989 describe specific compounds, the compounds are very poor in transparency and cannot be used for photography at all.